A foam core sandwich panel will be used, for example, as a structural material for forming airframes of airplanes. The foam core sandwich panel is formed by bonding together surface plates of a fiber-reinforced composite material with a foam synthetic resin core between them. The foam core sandwich panel is an excellent structural material useful for reducing weight and parts and free from a defect that permits water penetration in honeycomb core sandwich panels.
Although the foam core sandwich panel is an excellent structural material as mentioned above, it is possible that an interfacial crack between the surface plate and the core occurred in a part of the foam core sandwich panel propagates because the surface plates and the core are bonded. There has not been proposed any structure for preventing progressive delamination in the foam core sandwich panel.